Sintered magnet, method for producing powder for sintered magnet, and method for producing sintered magnet

Abstract

This sintered magnet comprises a first phase having a main phase of Sm-Fe-N-based crystal grains with a Th2Zn17-type structure and a second phase consisting of an alloy containing at least one or more elements selected from Group 2 elements and rare earth elements, the alloy having a temperature range of 180-620°C, wherein a residual magnetization is 10.0 kG or more.

Description

Sintered magnet, manufacturing method of powder for sintered magnet, and manufacturing method of sintered magnet

[0001] The present disclosure relates to an Sm—Fe—N based sintered magnet.

[0002] In recent years, Sm (samarium)-Fe (iron)-N (nitrogen) magnets have been developed as high-performance magnets. Sm-Fe-N compounds are known to have both high spontaneous magnetization and high anisotropy fields, as well as high heat resistance. However, because Sm-Fe-N compounds have the property of thermally decomposing at around 620°C, when obtaining a compact, it is not possible to heat powder of a magnetic material containing an Sm-Fe-N compound above the decomposition temperature. For this reason, when molding a sintered magnet using powder of an Sm-Fe-N compound, a method using a resin binder or a low-melting-point metal or alloy binder is known.

[0003] For example, Patent Document 1 describes Th2Zn 17 Type structure or Th2Ni 17 A technique is disclosed in which a modified powder containing Sm-Fe-N magnetic powder with a mold structure and at least one of metallic zinc or an alloy containing metallic zinc is prepared, and sintering is carried out so that the Sm-Fe-N magnetic powder meets a predetermined particle size, thereby improving the sintered density and increasing the magnetization.

[0004] In Patent Document 2, an attempt is made to improve magnetization by forming a coating containing zinc (Zn) on the surface of Sm—Fe—N crystal grains and further adding a low-melting-point alloy powder. Also, Patent Document 3 discloses a La—Cu—(Al, Mg, Zn) binder that has a low melting point, excellent wettability with the main phase, and excellent friability.

[0005] JP 2023-67693 A JP 2021-136347 A JP 2020-053435 A

[0006] However, the techniques described in Patent Documents 1 and 2 fail to achieve sufficient magnetization properties because the Zn component corrodes the Sm—Fe—N main phase and forms a low-magnetization phase. The binder described in Patent Document 3 does not ensure sufficient wettability, and a larger amount of binder than the main phase is required to densify the magnet. As a result, the magnetic properties of the Sm—Fe—N sintered magnet are not satisfactory.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a technique for improving magnetization in Sm—Fe—N sintered magnets.

[0008] The present disclosure has been made to solve at least one of the above-mentioned problems, and can be realized in the following forms.

[0009] <1> According to one aspect of the present disclosure, there is provided a sintered magnet. The sintered magnet is made of ThZn 17 The alloy comprises a first phase having Sm-Fe-N crystal grains having a Sm-Fe-N structure as a main phase, and a second phase made of an alloy containing at least one element selected from the group 2 elements and rare earth elements and having a melting point of 180°C or higher and 620°C or lower, and has a remanent magnetization of 10.0 kG or higher.

[0010] The alloy containing at least one element selected from the group 2 elements and rare earth elements has a composition that undergoes a eutectic reaction and has a low melting point. According to this type of sintered magnet, the melting point of the second-phase alloy is 180°C or higher and 620°C or lower, which is lower than the temperature at which Sm—Fe—N magnets undergo thermal decomposition (620°C or higher). Therefore, when sintering at temperatures lower than 620°C, the second-phase alloy can be used as a sintering aid, improving the sintered density of the first phase and suppressing the decrease in coercivity during the crystallization process. Furthermore, because the melting point of the second-phase alloy is 180°C or higher, it can also be used in devices that generate heat and reach high temperatures, such as motors for electric vehicles (EVs).

[0011] Furthermore, because this sintered magnet has a residual magnetization of 10.0 kG or more, it can be used in motors that require high rotation speeds and high torque, such as EV motors.

[0012] <2> According to one aspect of the present disclosure, there is provided a sintered magnet. This sintered magnet is made of ThZn 17 and a second phase consisting of a compound containing at least one Group 2 element, including oxygen, and having a melting point of 180°C or higher and 620°C or lower, and the remanence is 10.0 kG or higher.

[0013] It is known that Group 2 elements undergo a eutectic reaction with oxygen to lower the melting point, and therefore, even if a compound containing one or more Group 2 elements and oxygen is used, a second phase having a melting point of 180°C or higher and 620°C or lower can be obtained, and the same effects as those described above can be obtained.

[0014] <3> The sintered magnet of the above embodiment may further have a saturation magnetization of 11.5 kG or more. In this case, the magnet can be used in motors and the like that require even higher rotation speeds and torque, and the range of applications can be expected to expand.

[0015] <4> In the sintered magnet of the above embodiment, the second phase may satisfy at least one of the following conditions (1) and (2): (1) The content of the Group 2 element is 20 atomic % or more and 90 atomic % or less, and (2) The content of the rare earth element is 10 atomic % or more and 80 atomic % or less.

[0016] According to this embodiment of the sintered magnet, the second phase contains at least one of a Group 2 element and a rare earth element in the above-mentioned proportions. When the second phase is an alloy with the above-mentioned element contents, the melting point of the alloy that forms the second phase through a eutectic reaction can be further lowered, and the reactivity between the Sm—Fe—N crystal grains and the alloy can be improved while ensuring wettability with the Sm—Fe—N crystal grains. As a result, the sintered density can be increased and the magnetization can be improved.

[0017] <5> In the sintered magnet of the above aspect, the content of the second phase may be 20 vol% or less. In this way, the alloy that becomes the second phase can effectively function as an auxiliary agent for densifying the first phase while appropriately suppressing a decrease in the magnetization of the sintered magnet due to the second phase. As a result, the degree of densification during sintering can be further increased, and the magnetization of the sintered magnet can be further improved.

[0018] <6> In the sintered magnet of the above aspect, the content of the second phase may be less than 10 vol%. This allows the alloy that becomes the second phase to function more effectively as an auxiliary agent for densifying the first phase, while further suppressing the decrease in magnetization of the sintered magnet due to the second phase. As a result, the degree of densification during sintering can be further increased, and the magnetization of the sintered magnet can be further improved.

[0019] <7> According to another aspect of the present disclosure, there is provided a method for producing a powder for a sintered magnet used in molding the sintered magnet of the above aspect, the method for producing a powder for a sintered magnet including: a milling step of milling a coarse powder containing Sm—Fe—N single crystals to obtain the Sm—Fe—N crystal grains; an auxiliary powder preparation step of obtaining a powder of an alloy or compound that will become the second phase; and a mixing step of dispersing the Sm—Fe—N crystal grains and the powder of the alloy or compound to obtain the powder for a sintered magnet, the milling step, the auxiliary powder preparation step, and the mixing step being carried out in a low-oxygen concentration atmosphere.

[0020] This method for producing sintered magnet powder involves performing the above steps in a low-oxygen atmosphere, which suppresses oxidation of the Sm—Fe—N crystal grains and the alloy or compound powder, ensuring wettability between the Sm—Fe—N crystal grains and the alloy, resulting in the production of sintered magnets with remanence of 10.0 kG or greater.

[0021] <8> According to another aspect of the present disclosure, there is provided a method for producing a sintered magnet according to the above aspect, which includes a sintering step of pressure-sintering the powder for a sintered magnet produced by the method for producing a powder for a sintered magnet according to the above aspect at a sintering temperature of 600°C or less in an atmosphere with a low oxygen concentration.

[0022] According to this method for producing a sintered magnet, the thermal decomposition of the Sm—Fe—N main phase can be suppressed by setting the sintering temperature at 600°C or less, and the oxidation of the Sm—Fe—N crystal grains and alloy powder can be suppressed by performing this process in a low-oxygen atmosphere. As a result, the wettability between the Sm—Fe—N crystal grains and the alloy is ensured, improving the sintered density and magnetization of the sintered magnet, and enabling the production of a sintered magnet with a remanence of 10.0 kG or more.

[0023] The present disclosure can be realized in various forms, for example, in the form of a permanent magnet for a motor.

[0024] FIG. 1 is an explanatory diagram conceptually showing the cross-sectional structure of a sintered magnet of an embodiment; FIG. 2 is a process diagram showing an example of a method for producing a sintered magnet; FIG. 3 is a diagram showing evaluation results of a sample; FIG. 4 is a diagram showing the results of wettability evaluation of an alloy; FIG. 5 is a diagram showing an example of an SEM image of a sample; FIG. 6 is an explanatory diagram of a sample for SEM observation; and FIG. 7 is a diagram showing an example of an STEM image of a sample cross section and an EDX analysis result.

[0025] 1 is an explanatory diagram conceptually showing the cross-sectional structure of a sintered magnet 100 according to an embodiment. 17 The sintered magnet 100 comprises a first phase 10 whose main phase is Sm—Fe—N (samarium-iron-nitrogen) crystal grains having a Zn—Fe—N structure, and a second phase 20 made of an alloy containing at least one Group 2 element and / or rare earth element and having a melting point of 180°C or higher and 620°C or lower, or a compound containing at least one Group 2 element and oxygen and having a melting point of 180°C or higher and 620°C or lower. The remanence of the sintered magnet 100 is 10.0 kG or higher. The saturation magnetization of the sintered magnet 100 may be 11.5 kG or higher.

[0026] In Figure 1, the first phase 10 is hatched with diagonal lines that slope upward to the right, and the second phase 20 is hatched with diagonal lines that slope downward to the right. As shown in the figure, the first phase 10 has a plurality of Sm—Fe—N crystal grains 10G. The second phase 20 is located at the grain boundaries between the Sm—Fe—N crystal grains 10G and the Sm—Fe—N crystal grains 10G. The sintered magnet 100 may have voids V at the grain boundaries between the Sm—Fe—N crystal grains 10G and the Sm—Fe—N crystal grains 10G.

[0027] The main phase, Sm-Fe-N crystal grains 10G, is composed of Th2Zn 17 SmFe with type structure 17 N3. Sintered magnet 100 exhibits magnetism through Sm—Fe—N crystal grains 10G (main phase). The crystal structure of the main phase can be identified by, for example, subjecting sintered magnet 100 to X-ray diffraction analysis. The main phase refers to the compound that determines the properties of the sintered magnet.

[0028] SmFe 17 N3 has excellent saturation magnetization and a huge anisotropic magnetic field, so the sintered magnet 100 of this embodiment can withstand heat and reverse magnetic fields and generate a strong magnetic field.

[0029] The first phase 10 is composed of Sm—Fe—N-based crystal grains 10G, and is composed of ThNi. 17 The phase may include a structure different from the main phase, such as a TbCu7 type structure, a TbCu7 type structure, etc. Here, Tb is terbium, and Cu is copper.

[0030] The average grain size of the Sm—Fe—N crystal grains 10G of the first phase 10 is not particularly limited, but is preferably 0.1 μm or more and 20 μm or less, more preferably 0.4 μm or more and 10 μm or less, and even more preferably 1 μm or more and 5 μm or less. 17 The critical diameter of N3 single-domain particles is 0.356 μm, and a particle size equal to or greater than this critical diameter not only allows the powder to exist energetically in a stable state, but also allows for a sintered magnet with a higher density, resulting in improved magnetization.

[0031] The average particle size of the Sm—Fe—N crystal grains 10G of the first phase 10 in the sintered magnet 100 is approximately the same before and after sintering, so the Sm—Fe—N magnetic powder before sintering can be evaluated by using the volumetric results obtained using a dry particle size distribution measuring device, HELOS & RODOS (manufactured by Sympatec). 17 This is because, as mentioned above, Sm—Fe—N magnets having the α-type structure undergo thermal decomposition at temperatures above 620°C, and therefore the sintering temperature must be lower than this temperature, and the sintering process does not involve grain growth. The average grain size of Sm—Fe—N crystal grains 10G of first phase 10 in sintered magnet 100 can also be calculated using SEM (Scanning Electron Microscope) photographs.

[0032] The second phase 20 is composed of an alloy containing at least one of Group 2 elements and rare earth elements, or a compound containing at least one Group 2 element and oxygen. The Group 2 elements are elements belonging to Group 2 of the periodic table and include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The average particle size of the second-phase powder before sintering can be evaluated by employing the volumetric results obtained using a dry particle size distribution measuring device, HELOS & RODOS (manufactured by Sympatec). In addition, it can also be calculated using SEM (Scanning Electron Microscope) photographs.

[0033] The second phase 20 may contain elements other than the Group 2 elements, rare earth elements, and oxygen, such as silver (Ag), aluminum (Al), copper (Cu), and zinc (Zn).

[0034] Sm-Fe-N magnets are subject to sintering temperature restrictions because they undergo thermal decomposition at temperatures above 620°C, making it impossible to obtain high-density sintered bodies in the past. In contrast, in the sintered magnet 100 of this embodiment, the melting point of the alloy or compound that forms the second phase 20 is 620°C or lower, a temperature at which the main phase does not decompose. Therefore, when manufacturing the sintered magnet 100, the main phase does not decompose even when heated to a temperature at which the alloy melts. Therefore, by using an alloy of the above composition for the second phase 20, liquid phase sintering can occur, and SmFe 17 N3 / Sm2Fe 17 The second phase 20 made of the alloy or compound of the above composition can be formed as a grain boundary phase at the interface of N3. 17 The sintered magnet 100 has excellent wettability with N3. This allows for a dense sintered body to be obtained. As a result, the remanence can be increased to 10.0 kG or more. Furthermore, since the melting point of the alloy or compound that forms the second phase 20 is 180°C or higher, the sintered magnet 100 can be used in devices that generate heat and reach high temperatures, such as EV motors.

[0035] The melting point of the second phase can be measured using a DSC (differential scanning calorimeter). 10 to 20 mg of the liquid quenched foil obtained by melt spinning, which will be described later, is weighed out and used as the measurement sample. A BN (boron nitride) pan is used for the measurement, with the measurement temperature range set to room temperature to 700°C and the heating rate set to 10°C / min. The melting point is determined using the melting peak temperature that appears within the measurement temperature range.

[0036] The content of elements contained in the alloy or compound is not particularly limited, but it is preferable that at least one of the following (1) and (2) is satisfied: (1) The content of Group 2 elements is 20 atomic percent or more and 90 atomic percent or less, and (2) The content of rare earth elements is 10 atomic percent or more and 80 atomic percent or less.

[0037] When the alloy or compound is an alloy or compound combining these metal elements in the above ratio, the melting point can be further lowered by a eutectic reaction, and the reactivity between the first and second phases can be improved while ensuring wettability with the first phase, resulting in an increase in sintered density and improved magnetization.

[0038] The content of the second phase 20 is not particularly limited, but is preferably 0.1 vol% or more and 20 vol% or less, and more preferably less than 10 vol%. While the second phase 20 can act as an auxiliary agent for densifying the first phase 10, the alloy or compound of the second phase 20 is a nonmagnetic component. Therefore, if the second phase 20 is contained in a large amount, the proportion of the magnetic phase may relatively decrease, resulting in a risk of reduced magnetization. When the content of the second phase 20 is 20 vol% or less, the second phase 20 can effectively function as an auxiliary agent for densifying the first phase 10 while appropriately suppressing the reduction in magnetization of the sintered magnet 100 due to the second phase 20. As a result, the degree of densification during sintering can be further increased, and the magnetization of the sintered magnet 100 can be further improved. When the content of the second phase 20 is less than 10 vol%, the second phase can act more effectively, further improving the sintered density and magnetization of the sintered magnet.

[0039] The sintered magnet 100 may contain unavoidable impurity elements, etc., to the extent that the magnetic properties of the main phase are not impaired. An unavoidable impurity element is an impurity element whose inclusion cannot be avoided during the production, etc., of the sintered magnet 100 of the embodiment, or whose avoidance would result in a significant increase in production costs. Examples of such unavoidable impurity elements include impurity elements in raw materials and elements contained in lubricants, etc. used during molding.

[0040] Fig. 2 is a process diagram showing an example of a method for manufacturing a sintered magnet 100. The method for manufacturing the sintered magnet 100 of this embodiment is not particularly limited, but it can be manufactured, for example, by the following method. As shown in Fig. 2, in the method for manufacturing the sintered magnet 100, steps P0 for manufacturing a powder for a sintered magnet and P4 for sintering are carried out in this order. In the step P0 for manufacturing a powder for a sintered magnet, steps P1 for grinding, P2 for preparing an auxiliary powder, and P3 for mixing are carried out in this order.

[0041] In the crushing step P1, Th2Zn 17 Coarse powder containing Sm—Fe—N single crystals having a crystalline structure is pulverized to obtain Sm—Fe—N crystal grains. 17 The average particle size of the Sm—Fe—N crystal grains after pulverization is not particularly limited, but is preferably 0.1 μm to 20 μm, more preferably 0.4 μm to 10 μm, and even more preferably 1 μm to 5 μm.

[0042] In the auxiliary powder preparation process P2, powder of a predetermined size of the alloy or compound that will become the second phase is prepared to obtain the auxiliary powder. For example, the auxiliary powder can be prepared by the method described in the examples below. The method for preparing the auxiliary powder is not limited to the method described in the examples below. For example, a gas atomization method or a thermal plasma method may also be used.

[0043] In the mixing step P3, the Sm—Fe—N crystal grains and the auxiliary powder are dispersed to obtain a mixed powder for a sintered magnet. The mixing step P3 may be a wet method in which the Sm—Fe—N crystal grains and the auxiliary powder are dispersed in a solvent (e.g., ethanol), or a dry method in which the Sm—Fe—N crystal grains and the auxiliary powder are dispersed in an inert gas (e.g., argon gas, helium gas, nitrogen gas, etc.).

[0044] The above-mentioned grinding process P1, auxiliary powder preparation process P2, and mixing process P3 are all performed in a low-oxygen atmosphere. The oxygen concentration is adjusted by controlling the atmosphere in each process. A low-oxygen concentration is a concentration lower than the oxygen concentration in the atmosphere (approximately 21 vol%). The oxygen concentration is, for example, preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 0.5 ppm or less. For example, a low-oxygen atmosphere can be achieved by injecting an inert gas into a vacuum chamber. Performing the above processes in a low-oxygen atmosphere can prevent oxidation of the Sm—Fe—N crystal grains and auxiliary powder, ensuring wettability between the Sm—Fe—N crystal grains and alloy powder. However, even in a low-oxygen atmosphere, trace amounts of oxygen are present, and oxidation proceeds very slowly over time. The auxiliary powder made of a compound containing one or more Group 2 elements and containing oxygen can be produced, for example, by preparing the auxiliary powder in an atmosphere of low oxygen concentration, and then leaving the powder in the atmosphere of low oxygen concentration for a long period of time (1 hour to 10 weeks), thereby allowing oxidation to proceed to a certain extent.

[0045] In the sintering step P4, the sintered magnet powder produced in the sintered magnet powder production step P0 is molded and pressure-sintered at a sintering temperature of 600°C or less in a low-oxygen atmosphere. In the sintering step P4, firing is performed in an atmosphere with an oxygen concentration similar to that of the crushing steps P1 to P3. By setting the sintering temperature to 600°C or less, thermal decomposition of the Sm—Fe—N crystal grains can be suppressed. Furthermore, by performing the sintering step P4 in a low-oxygen atmosphere, oxidation of the Sm—Fe—N crystal grains and alloy powder can be suppressed. As a result, the density can be improved, and the magnetization of the sintered magnet 100 can be improved.

[0046] The sintered magnet of this embodiment can be used as a permanent magnet for various motors, such as motors for EVs, motors built into robots, motors built into drones, and motors for elevators.

[0047] The present disclosure will be explained in more detail with reference to examples. FIG. 3 shows the evaluation results for Samples 1 to 17. The remanent magnetization Br and saturation magnetization Js were evaluated for Samples 1 to 17 of sintered magnet 100, each with a different second phase 20 composition. In FIG. 3, of the elements contained in the second phase 20, Group 2 elements and rare earth elements are indicated by double-lined frames. In the examples, calcium (Ca) and barium (Ba) are used as Group 2 elements, and lanthanum (La), samarium (Sm), and praseodymium (Pr) are used as rare earth elements.

[0048] 1. Manufacturing of Samples Samples 1 to 17 were manufactured by the manufacturing method exemplified in the above embodiment (FIG. 2).

[0049] (1) Pulverization step P1: As a coarse powder containing Sm—Fe—N single crystals, SmFe with an average particle size of 30 μm 17 N3 powder was used. First, in a glove box with an oxygen concentration controlled to 0.5 ppm or less, stainless steel balls and the above coarse powder were placed in a stainless steel pot, and ethanol was added as a solvent. The pot was rotated, and the coarse powder was ball milled. The rotation time was 48 hours and the rotation speed was 120 rpm. The slurry obtained by the above process was sieved through a 25 μm mesh sieve in the same glove box and dried in a vibration dryer. The resulting powder was then sieved through a 250 μm mesh sieve to obtain Sm—Fe—N crystal grains as a dry powder. The average particle size of the Sm—Fe—N crystal grains obtained by this process was 0.1 μm or more and 20 μm or less. Here, the particle size distribution was measured by dry measurement.

[0050] (2) Auxiliary Agent Powder Preparation Process P2 The following materials were used as raw materials (granular alloy raw materials) for the alloy powder: Ca metal (granular), Ba metal (granular), Cu metal (granular), Ag metal (granular), Zn metal (granular), Al metal (granular), La metal (granular), Sm metal (granular), and Pr metal (granular).

[0051] These granular alloy raw materials were weighed to obtain the composition ratio shown in Figure 3 and melted in an arc melting furnace under reduced pressure of argon (Ar) to produce alloy ingots. The produced ingots were cut into chips using a grinder in a glove box with an oxygen concentration controlled to 0.5 ppm or less, to obtain coarse alloy powder. 0.5 g of the obtained coarse alloy powder, stainless steel balls, and acetonitrile were placed in a stainless steel pot and milled in a planetary ball mill at a rotation speed of 200 rpm for 6 hours.

[0052] The slurry obtained by the above process was sieved through a 25 μm mesh sieve in the same glove box and dried in a vibration dryer. The resulting powder was then sieved through a 63 μm, 40 μm, 20 μm, or 7 μm mesh sieve to obtain a dried alloy powder. The alloy powder had an average particle size of 0.1 μm or more and 20 μm or less. By setting the average particle size of the alloy powder to 0.1 μm or more and 20 μm or less, the dispersibility of the alloy particles in the sintered body structure can be improved, allowing the alloy powder to act as a sintering aid over a wider range, and improving the sintered density and magnetization.

[0053] The auxiliary powder used to prepare Sample 17 was obtained by leaving the Ba-Cu alloy powder obtained by the above process in an atmosphere with an oxygen concentration of 0.5 ppm for two weeks to allow for slow oxidation. Figure 7 shows an STEM image of a cross section of Sample 17 and an element distribution profile along line X-X' measured by energy dispersive X-ray analysis. Oxygen was detected in the second phase along with Ba and Cu. The cross section of Sample 17 was prepared by processing using a focused ion beam (FIB) in a vacuum and then subjected to STEM observation while the vacuum was maintained. Therefore, it can be said that the detected oxygen was contained in the second phase and not due to oxidation of the processed cross section.

[0054] (3) Mixing step P3: The Sm—Fe—N crystal grains (SmFe) obtained in the pulverization step P1 are mixed. 17The auxiliary powder obtained in the auxiliary powder preparation step P2 and the Sm-Fe-N system crystal grains (SmFeN) were ball milled using ethanol as a solvent to obtain a mixed powder (slurry) for a sintered magnet. In the mixing step P3, the auxiliary powder was added so that the second phase content (vol%) shown in Table 3 was obtained. The amount of auxiliary powder added (vol%) was approximately equal to the second phase content (vol%), and the Sm-Fe-N system crystal grains (SmFeN) were formed. 17 The amount (volume) of auxiliary powder relative to the amount of auxiliary powder added to the amount of N3).

[0055] (4) Sintering Step P4 The sintered magnet powder obtained in the mixing step P3 was placed in a non-magnetic carbide die (mold) in a glove box with an oxygen concentration controlled to 0.5 ppm or less. A magnetic field of 2 T was applied to the powder using a compacting magnetic field press device that integrated a hydraulic press and a magnetic field orientation device, without exposing the powder to the atmosphere. A pressure of 600 MPa to 1200 MPa was then applied to the mixed powder for press molding. This was then electrically sintered in a vacuum atmosphere at a sintering temperature of 300°C to 600°C for 1 to 10 minutes. This resulted in the formation of Sm—Fe—N crystal grains (SmFe 17 The resulting sintered body (sintered magnet 100) included a first phase 10 composed primarily of N, and a second phase 20 composed of an auxiliary agent. Sintering was performed under appropriate conditions (sintering temperature and sintering time) depending on the sample.

[0056] 2. Evaluation Method (1) Evaluation of Magnetic Properties of Sintered Body The residual magnetization Br and saturation magnetization Js of the sintered body were measured using a vibrating sample magnetometer (VSM). 17 Since N3 has a very large anisotropy magnetic field of 260 kOe and it is difficult to completely saturate it, a magnetic field of up to 9 T (90 kOe) was applied using a VSM, and the saturation magnetization Js9 T at that point was used as the evaluation value. (2) Density evaluation of sintered body The density of the sintered body was measured in pure water using the Archimedes method. The density of the sintered body was measured by the Archimedes method using the Sm2Fe 17 The theoretical density of N is 7.67 g / cm 3 The relative density was evaluated as an index of compactness, but since the specific gravity of the second phase alloy differs, this is only a reference value.

[0057] In order to perform a more substantial density evaluation of the sintered body, SEM images of a cross section formed by ion milling were taken using SEM observation sample 100S (described below), and image analysis was performed by binarization using image processing software Image-J. The image processing method is described below. The SEM images used to calculate the volume fraction of the first phase were taken in an area (wider than 70 μm × 45 μm) at a display magnification of 3000 times or less on the SEM device. Figure 5 shows an example of an SEM image of a sample. Figure 5(A) shows an image binarized so that the white areas represent voids V. Figure 5(B) shows an image binarized so that the white areas represent the second phase 20. The SEM images of each sample were binarized. The threshold values ​​for the binarization process were determined by setting 0 to black and 255 to white, with reference to section 28.2.4 Threshold in the Image 1.46 ver. manual, with the Auto Threshold method set to default. The area ratio of the first phase 10 was determined by subtracting the sum of the area ratios of the voids V and the second phase 20 obtained by this binarization process from 100%. Based on stereology, the calculated area ratio was assumed to be equal to the volume ratio, and the volume ratio of the first phase 10 was calculated. The same process was performed on five different fields of view for each sample to calculate the volume ratio of the first phase 10, and the average value was used as the first phase volume ratio for each sample. In Figure 5, only some of the voids V and second phases 20 are indicated by symbols.

[0058] 3. Measurement Results As shown in Figure 3, Samples 1 to 11, 16, and 17 have a remanent magnetization Br of 10.0 kG or more. Samples 1 to 11, 16, and 17 meet the following requirements [1] to [3] (Figure 3). [1] Th2Zn 17 It includes a first phase whose main phase is Sm—Fe—N-based crystal grains having a Zn-Fe—N structure. [2] It includes a second phase consisting of an alloy containing at least one element selected from the group 2 elements and rare earth elements and having a melting point of 180°C or higher and 620°C or lower, or a compound containing at least one element selected from the group 2 elements and oxygen and having a melting point of 180°C or higher and 620°C or lower. [3] It has a remanent magnetization Br of 10.0 kG or higher.

[0059] Samples 1 to 11, 16, and 17 satisfied the requirement [2] above, allowing the Sm—Fe—N crystal grains to undergo liquid phase sintering, resulting in dense sintered bodies (sintered magnets). Furthermore, Samples 1 to 11, 16, and 17 satisfied the requirement [2] above, allowing the alloy or compound forming the second phase to exhibit excellent wettability with the Sm—Fe—N crystal grains. As a result, the remanence Br was able to be increased to 10.0 kG or more (satisfying the requirement [3] above).

[0060] In contrast, Samples 12 to 15 do not satisfy the above requirement [2], and as a result, sufficient magnetization cannot be obtained, and therefore, the requirement [3] is not satisfied. Sample 12 does not have a second phase, and the remanent magnetization Br = 9.98 kG, and does not satisfy the requirement [3]. Samples 13 to 15 contain alloys that form the second phase with melting points of 180 ° C or higher and 620 ° C or lower, but do not contain any Group 2 elements or rare earth elements, and the remanent magnetization Br is < 10.0 kG (does not satisfy the requirement [3]).

[0061] Sample 13 uses zinc (Zn) as the second phase. Compared to Sample 12, it has a higher relative density and a higher saturation magnetization Js, but a lower remanent magnetization Br. The Zn component reacts with the Sm—Fe—N main phase to form a low-magnetization phase, presumably resulting in a lower remanent magnetization Br. Sample 14 uses an alloy of zinc (Zn) and tin (Sn) as the second phase. Compared to Sample 12, it has a higher relative density, but its saturation magnetization Js is equivalent to that of Sample 12, and its remanent magnetization Br is lower. Sample 15 uses an alloy of aluminum (Al) and tin (Sn) as the second phase. Compared to Sample 12, it has a similar relative density, but its saturation magnetization Js and remanent magnetization Br are lower. Thus, when a metal containing neither a Group 2 element nor a rare earth element was used as the second phase, the magnetization could not be improved compared to when no second phase was present.

[0062] Although Samples 4 and 10 contain zinc (Zn) in the second phase, both the remanent magnetization Br and the saturation magnetization Js are improved compared to Samples 13 and 14. This result also confirms that the magnetization can be improved by including at least one element selected from the group 2 elements and rare earth elements in the second phase.

[0063] Samples 1 to 11, 16, and 17 further satisfy the following requirement [4]. [4] The saturation magnetization Js is 11.5 kG or more. As described above, Samples 1 to 11, 16, and 17 exhibited improved remanent magnetization Br and saturation magnetization Js compared to Sample 12, which did not have the second phase 20, and Samples 13 to 15, which did not have the second phase 20 and contained no Group 2 elements or rare earth elements. Furthermore, Samples 1 to 11 exhibited improved relative density and main phase ratios as determined by binarization processing compared to Sample 12, which did not have the second phase 20.

[0064] Samples 2 to 11, 16, and 17 further satisfy the following requirement [5]. [5] The second phase satisfies at least one of the following requirements (I) and (II): (I) The content of the Group 2 element is 20 atomic % or more and 90 atomic % or less. (II) The content of the rare earth element is 10 atomic % or more and 80 atomic % or less. Samples 2 to 11, 16, and 17 contain at least one of the Group 2 element and the rare earth element in the above proportions in the second phase. When the second phase has the above element contents, the melting point of the alloy or compound that forms the second phase by the eutectic reaction can be further lowered, and the reactivity between the Sm—Fe—N crystal grains and the auxiliary particles can be improved while ensuring wettability with the Sm—Fe—N crystal grains. As a result, Samples 2 to 11, 16, and 17 were able to improve the saturation magnetization Js while maintaining the remanence Br, compared to Sample 1.

[0065] Samples 3, 7 to 11, 16, and 17 also satisfy the following requirement [6]. [6] The content of the second phase is 20 vol% or less. Because Samples 3, 7 to 11, 16, and 17 satisfy requirement [6] above, they are able to effectively use the alloy or compound that becomes the second phase as an auxiliary agent for densifying the first phase, while appropriately suppressing the decrease in magnetization of the sintered magnet caused by the second phase. As a result, the degree of densification during sintering was further increased, and the remanence Br and saturation magnetization Js of the sintered magnet were further improved compared to Samples 1, 4 to 6.

[0066] Samples 16 and 17 also satisfy the following requirement [7]. [7] The content of the second phase is less than 10 vol%. Because Samples 16 and 17 satisfy requirement [7] above, they are able to further suppress the decrease in magnetization of the sintered magnet due to the second phase, while allowing the alloy or compound that becomes the second phase to function more effectively as an auxiliary agent for densifying the first phase. As a result, the degree of densification during sintering could be further increased, and the remanence Br and saturation magnetization Js of the sintered magnets could be further improved compared to Samples 3 and 7 to 11.

[0067] As explained above, Samples 1 to 11, 16, and 17 fulfill all of the requirements [1] to [3] above and are examples of the sintered magnet 100 of the above embodiment. These samples had high remanent magnetization of 10.0 kG or more, and were sintered magnets with higher magnetization than Samples 12 to 15.

[0068] 4. Wettability of the Alloy Prior to the production of the above samples, Sm—Fe—N crystal grains (SmFe 17 A preliminary experiment was conducted to narrow down the element group and alloy composition that exhibit good wettability with Sm-Fe-N system crystal grains (SmFeN). Figure 4 shows the results of the alloy wettability evaluation. The alloy powder with the composition shown in Figure 4 was produced by (2) alloy powder production step P2 of the manufacturing method of the above sample. 17 The Sm-Fe-N crystal grains (SmFeN fine powder) were prepared by the (1) pulverization step P1 of the manufacturing method of the above sample. 17The alloy powder was added at a ratio of 20 vol% to Sm-Fe-N fine powder, and the powder was subjected to electric pressure sintering at a sintering temperature of 450°C to 600°C, for 10 minutes, at a pressure of 600 MPa, in a vacuum atmosphere. The porosity was calculated using the sintered bodies (samples S1 to S19), and these values ​​were compared for each alloy to determine the Sm-Fe-N system crystal grains (SmFe 17 An alloy composition with good wettability to the N3 fine powder was selected.

[0069] FIG. 6 is an explanatory diagram of sample 100S for SEM observation. First, the sintered body (sintered magnet) produced by the above method was cut into a cylindrical shape with a diameter of 10 mm and a thickness of 3 mm ( FIG. 6(A) ). Then, a cross section was exposed using waterproof abrasive paper ( FIG. 6(B) ). The cross section was subjected to Ar ion milling to produce sample 100S for SEM observation ( FIG. 6(C) ). SEM observation was performed using sample 100S for SEM observation, and secondary electron images at 1000x magnification were taken at five different points in the field of view. The captured secondary electron images were binarized using image processing software Image-J to calculate the porosity.

[0070] As shown in Figure 4, the metal binders of samples S1 to S4 contain calcium (Ca), a Group 2 element; the metal binders of samples S5 and S6 contain barium (Ba), a Group 2 element; the metal binders of samples S7, S8, and S11 contain lanthanum (La), a rare earth element; and the metal binders of samples S9 and S10 contain praseodymium (Pr), a rare earth element. The metal binders of samples S12 to S18 contain neither a Group 2 element nor a rare earth element. The sintered compact of sample S19 does not contain a metal binder.

[0071] Preliminary experiments confirmed that the porosity was significantly reduced in the sintered bodies (samples S1 to S11) to which a metal binder containing a Group 2 element and a rare earth element was added. That is, the metal binder of samples S1 to S11 was used to form Sm-Fe-N crystal grains (SmFe 17 It is believed that it exhibits good wettability with respect to the surface of the SiO2 nanoparticles (N3 fine powder).

[0072] In the preliminary experiments, calcium (Ca) and barium (Ba) were used as the Group 2 elements, but for the following reasons, it is believed that similar effects can be obtained by using other Group 2 elements such as beryllium (Be), magnesium (Mg), strontium (Sr), and radium (Ra).

[0073] In the Ellingham diagram, calcium (Ca) is located below Sm, so Ca has the effect of reducing Sm over the entire temperature range. 17 It is also used as a reducing material for Sm oxide when chemically synthesizing N3 particles. 17 Since Ca is an element that undergoes a redox reaction with the inevitable oxides present on the particle surface with a N3-based main phase, alloys or compounds containing Ca where the oxidation state of Ca is not saturated also have a similar effect. "Occurrence of a redox reaction" can be rephrased as "having a certain level of reactivity with the main phase particle surface," and wettability can also be considered one aspect of this reactivity. Ca belongs to Group 2 of the periodic table, and its homologous elements, Be, Mg, Sr, Ba, and Ra, also have a reducing effect on Sm—Fe—O. Therefore, similar effects can be expected with other elements in the same group as Ca. In addition, in binary phase diagrams, element X (Be, Mg, Sr, Ba, and Ra) have a eutectic point when alloyed with Ca, and can achieve the minimum low melting point required for a binder.

[0074] In addition, in the preliminary experiments, lanthanum (La) and praseodymium (Pr) were used as rare earth elements, but for the following reasons, it is believed that similar effects can be obtained by using other rare earth elements such as scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0075] The main phase particles are Sm2Fe17 As shown in the composition of N3, it contains the rare earth element Sm. Sm and other lanthanoid elements (such as La and Pr) are expected to exhibit high similarity / substitution properties and high reactivity, as they form a complete solid solution system. In fact, it has been experimentally demonstrated that one of the reactivity properties is good wettability.

[0076] Therefore, the inventors aimed to improve the volume fraction of the first phase (magnetic phase) by optimizing the composition and the amount of addition of an alloy containing at least one of a Group 2 element and a rare earth element.

[0077] The present disclosure has been described above based on embodiments and examples, but the embodiments of the above-described aspects are intended to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present disclosure. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0078] The present disclosure can also be realized as the following application examples. [Application Example 1] A sintered magnet comprising: ThZn 17 A sintered magnet comprising: a first phase consisting primarily of Sm—Fe—N crystal grains having a ThZn type structure; and a second phase consisting of an alloy containing at least one element selected from the group 2 elements and rare earth elements, the alloy having a melting point of 180°C or higher and 620°C or lower, the second phase having a remanent magnetization of 10.0 kG or higher. 17A sintered magnet comprising: a first phase mainly composed of Sm—Fe—N crystal grains having the formula: and a second phase consisting of a compound containing one or more Group 2 elements, including oxygen, and having a melting point of 180°C or higher and 620°C or lower, wherein the sintered magnet has a remanent magnetization of 10.0 kG or higher. [Application Example 3] The sintered magnet according to Application Example 1 or 2, further characterized in that the saturation magnetization is 11.5 kG or higher. [Application Example 4] The sintered magnet according to any one of Application Examples 1 to 3, wherein the second phase satisfies at least one of the following (1) and (2): (1) the content of the Group 2 element is 20 atomic % or higher and 90 atomic % or lower; (2) the content of the rare earth element is 10 atomic % or higher and 80 atomic % or lower. [Application Example 5] The sintered magnet according to any one of Application Examples 1 to 4, characterized in that the content of the second phase is 20 vol% or less. [Application Example 6] The sintered magnet according to any one of Application Examples 1 to 5, characterized in that the content of the second phase is less than 10 vol%. [Application Example 7] A method for producing a powder for a sintered magnet used in molding the sintered magnet according to any one of Application Examples 1 to 6, comprising: a milling step of milling a coarse powder containing Sm—Fe—N single crystals to obtain Sm—Fe—N crystal grains; an auxiliary powder preparation step of preparing a powder of an alloy or compound that will become the second phase; and a mixing step of dispersing the Sm—Fe—N crystal grains and the powder of the alloy or compound to obtain the powder for the sintered magnet, which is a mixed powder, characterized in that the milling step, the auxiliary powder preparation step, and the mixing step are carried out in a low-oxygen concentration atmosphere. [Application Example 8] The method for producing a sintered magnet according to any one of Application Examples 1 to 6, further comprising a sintering step of pressure-sintering the powder for a sintered magnet produced by the method for producing a powder for a sintered magnet according to Application Example 7 at a sintering temperature of 600°C or less in an atmosphere with a low oxygen concentration.

[0079] 10...First phase 10G...Sm-Fe-N crystal grains 20...Second phase 100...Sintered magnet 100S...Sample for SEM observation V...Void

Claims

1. A sintered magnet, comprising Th2Zn 17 A sintered magnet comprising: a first phase whose main phase is Sm—Fe—N crystal grains having a Zn—Fe—N structure; and a second phase made of an alloy containing at least one element selected from the group 2 elements and rare earth elements, and having a melting point of 180°C or higher and 620°C or lower, wherein the sintered magnet has a remanent magnetization of 10.0 kG or higher.

2. A sintered magnet, comprising Th2Zn 17 and a second phase consisting of a compound containing at least one Group 2 element, including oxygen, and having a melting point of 180°C or higher and 620°C or lower, wherein the sintered magnet has a remanent magnetization of 10.0 kG or higher.

3. A sintered magnet according to claim 1 or 2, further characterized in that the saturation magnetization is 11.5 kG or more.

4. A sintered magnet according to claim 1 or 2, characterized in that the second phase satisfies at least one of the following conditions (1) and (2): (1) The content of Group 2 elements is 20 atomic percent or more and 90 atomic percent or less, and (2) The content of rare earth elements is 10 atomic percent or more and 80 atomic percent or less.

5. A sintered magnet according to claim 1 or 2, characterized in that the content of the second phase is 20 vol % or less.

6. A sintered magnet according to claim 1 or 2, characterized in that the content of the second phase is less than 10 vol %.

7. A method for producing powder for sintered magnets used in molding the sintered magnets described in claim 1 or 2, comprising: a milling step of milling coarse powder containing Sm-Fe-N single crystals to obtain Sm-Fe-N crystal grains; an auxiliary powder preparation step of preparing a powder of an alloy or compound that will become the second phase; and a mixing step of dispersing the Sm-Fe-N crystal grains and the powder of the alloy or compound to obtain the powder for sintered magnets, which is a mixed powder; wherein the milling step, the auxiliary powder preparation step, and the mixing step are carried out in an atmosphere with a low oxygen concentration.

8. A method for producing a sintered magnet as set forth in claim 1 or claim 2, characterized in that it comprises a sintering step in which the powder for a sintered magnet produced by the method for producing a powder for a sintered magnet as set forth in claim 7 is pressure-sintered at a sintering temperature of 600°C or less in an atmosphere with a low oxygen concentration.

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